Conventional methods of jointing adjacent members include riveting, welding, bolt-nut jointing, etc. . .
In the riveting and bolt-nut jointing methods which utilize compressive force applied to mated flanges in directions toward each other, bolts or rivets are placed in a state of tension in their axial direction, the tension being equal to the compressive force, because the riveting or the tightening of the bolts is performed after the flanges have been brought into intimate contact with each other. Further, the compressive force acting on the rivet or bolt portions of the mated flanges does not act equally on portions of the flanges other than the portions having rivets or bolts. To overcome this problem, it is usual to make the thickness of the flange large enough to provide sufficient rigidity thereto. In a case where a fluid pressure acts on the mating surfaces of the flanges, however, leakage of the fluid from the mated surfaces occurs because the unbalance in pressure distribution on the surfaces cannot completely be avoided even by increasing the thickness of the flanges or attempts to uniformly distribute the tightening pressure on the mated flanges. This is because the flange portions may be resiliently deformed between the riveted or bolted areas by external forces.